The present invention relates to an electrophotographic recording material comprising an electrically conductive base material, an optional insulating intermediate layer, and a photoconductive double layer comprised of a charge-generating and a charge-transporting layer, the latter layer comprising a pyrimido[5',4':5,6]-pyrido[1,2-a]benzimidazole derivative as transport compound, binders and dyes or pigments.
The known high-sensitivity photoconductor systems based on organic substances are predominantly present in double or multiple layer arrangements which consist, in the majority of cases, of a relatively thin layer that absorbs within the visible wavelength region and is capable of charge generation and, adjacent thereto, a thicker charge-transporting layer that is transparent to visible light.
By virtue of their layered structure and the chemical nature of the charge transport compounds, these photoconductor double layers have a high photosensitivity upon negative or, where appropriate, upon positive electrostatic charging. By choosing suitable dyes or pigments as sensitizers, it is possible to affect the spectral photosensitivity of these double layers.
Photoconductor double layers are also known in which inorganic and organic substances are combined by means of a layered structure in which conductive base materials support layers of selenium, poly-N-vinyl-carbazole and selenium (see German Auslegeschrift No. 2,364,967, which corresponds to U.S. Pat. No. 3,915,076). Using such a layer it is possible to obtain sufficient photosensitivity for both polarities.
There have also been disclosed photoconductor double layers for black/red reproduction that combine a plurality of photoconductive layers and materials having different absorption regions (for example, a red-sensitive photoconductive layer having a .lambda. greater than 600 nm, a non-red-sensitive photoconductive layer having a .lambda. less than 600 nm and a red- and non-red-sensitive photoconductive layer), to provide positively and negatively chargeable systems which are sensitive in different spectral regions. (See German Offenlegungsschrift No. 2,938,129, which corresponds to U.S. Pat. No. 4,521,504.)
A disadvantage to such systems is their multi-layered structure, involving partly inorganic components that lead to mutual adhesion problems and need to be applied by different methods.
In German Patent Application No. P35 02 681.2 (filed Jan. 26, 1985), attention is drawn to the high photosensitivity, on positive electrostatic charging, of the described transport compounds. The photosensitivity in question is extended by self-absorption of the compound up to a wavelength of about 500 nm, and by the addition of suitable dyes that effect spectral expansion it can be further extended.